In various industrial and other areas, it is often desirable, and sometimes necessary, to control the flow of the medium to be pumped ("pumped medium") as a function of the prevailing pressure of the pumped medium. For example, where the pumped medium is contained in a reservoir or tank that itself receives a varying supply, the maintenance of a selected fill level requires increasing the pumping rate when the level tends to rise and reducing the pumping rate when the level tends to fall. The pumped medium may be not only water and other liquids but solutions and suspensions of various kinds.
At present, such pumping is controlled by sensors monitoring the pressure of the medium being pumped at the inflow side of the pump. The sensors control the pumping rate of pumps whose capacity may be varied, e.g., piston pumps with a variable stroke rate. Such monitors may cease functioning without the pump necessarily stopping. This results in the pump pumping either too much or too little, possibly resulting in severe consequences with regard to safety. In case safety is decisive, double safety measures have to be incorporated into the design, e.g., by providing duplicate sensors, which will make the pump more expensive and more prone to succumb to electrical faults.